Perhaps you should try some spelling variations:
dan thanh » dang thanh, danh thanh, van thanh
ban thanh » ban hanh, ban hang
hieu van » hieu va, thien van, lieu va
cam thuc » am thuc, cam thu, can thuc
nam thuc » nam thuoc, am thuc, nam thu
so sach » so sanh, bo sach, co sach
nang ma » tang ma, sang ma, nang cao
y nang » ky nang, ly nang, v nang
ma hoi » mai hoi, xa hoi, ma hoa
cua tu » cua tuc, cua su, cua cu

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: so sach y nang ma hoi. hieu van ((cam thuc) OR (nam thuc)) ((dan thanh) or (ban thanh)) dai cua tu~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so sach y nang ma hoi. hieu van ((cam thuc) OR (nam thuc)) ((dan thanh) OR (ban thanh)) dai cua tu.
• The words AND, OR and NOT may confuse the search; try adding quotes: "so sach y nang ma hoi. hieu van ((cam thuc) OR (nam thuc)) ((dan thanh) or (ban thanh)) dai cua tu".
• Adding a wildcard symbol may retrieve word variants: so sach y nang ma hoi. hieu van ((cam thuc) OR (nam thuc)) ((dan thanh) or (ban thanh)) dai cua tu*.